Peptide

AOD-9604 is a synthetic copy of the last fifteen amino acids of growth hormone, with a tyrosine stuck on the front. The idea, worked out at Monash University in the 1990s, is that this is the part of growth hormone that burns fat, separated from the parts that raise IGF-1 and blood sugar. In obese mice it reduced weight gain and fat mass and raised fat oxidation and energy expenditure; none of these studies measured IGF-1, so the separation the molecule is named for has not actually been demonstrated. It was developed for obesity by Metabolic Pharmaceuticals and abandoned. No trial of AOD-9604 in humans for weight, fat or anything else appears in the published literature — the human evidence for it is adipose tissue in a dish.

BPC-157 is a synthetic 15-amino-acid peptide, a fragment of a protein found in human gastric juice. Clinicians and athletes increasingly use it for musculoskeletal injuries. In rats it consistently speeds healing of many tissues. Human data amount to three small, uncontrolled pilot reports, all by the same first author. It is not approved by the FDA and is banned in professional sport.

Bremelanotide (PT-141, Vyleesi) is a cyclic seven-amino-acid analog of α-MSH that activates melanocortin receptors in the brain, chiefly MC4R. It is approved in the US for low sexual desire (hypoactive sexual desire disorder) in premenopausal women, based on two phase 3 trials of 1,267 women in which an as-needed 1.75 mg injection modestly increased desire and reduced distress. It was first developed as a nasal spray for erectile dysfunction, where it produced erections in men who did not respond well to sildenafil. Nausea affects about 40% of users.

Cartalax is the tripeptide Ala-Glu-Asp (AED), one of the short "peptide bioregulators" developed by Vladimir Khavinson's group in St Petersburg and promoted for cartilage. In cell cultures it switched on cartilage-forming genes in aging human stem cells and lowered markers of aging in chondrocytes. There are no published human trials, and almost every study comes from the developers' own group.

CJC-1295 is GHRH(1-29) with four amino acid substitutions and a maleimide group that makes it latch permanently onto albumin in the bloodstream, stretching a peptide with a four-minute half-life into one lasting almost a week. In the one published human trial, single subcutaneous doses raised growth hormone 2- to 10-fold for six days or more and IGF-1 1.5- to 3-fold for 9-11 days, with an estimated half-life of 5.8-8.1 days. That is the entire human efficacy literature: 28- and 49-day dose-ranging studies in healthy volunteers, with no measurement of muscle, fat, strength or anything else clinical. Confusingly, most of what is sold as "CJC-1295" is the version without the albumin-binding group, which is simply modified GHRH(1-29) and lasts hours, not days.

DSIP is a nine-amino-acid peptide pulled out of the cerebral venous blood of sleeping rabbits in Basel in 1977 and named for what its discoverers thought it did. Unusually for a peptide sold online, it was actually tested in people: several small controlled trials in insomniacs through the 1980s, all using intravenous doses of 25 nmol/kg. The early results were encouraging and the later, better-controlled ones were not — one concluded sleep improvement was "of little clinical significance" and a 1992 double-blind study found the effects weak, partly an artifact of the placebo group, and "not likely to be of major therapeutic benefit". Nearly fifty years on, no DSIP gene, precursor protein or receptor has been identified, and a 2006 review called the sleep hypothesis "extremely poorly documented and still weak". Its plasma half-life in dogs is four minutes.

Elamipretide (SS-31) is a four-amino-acid peptide that concentrates in the inner mitochondrial membrane and binds cardiolipin, a membrane lipid that mitochondria need to form their inner folds (cristae). In September 2025 the US FDA gave it accelerated approval, as Forzinity, to improve muscle strength in Barth syndrome. Its randomized trials have mostly missed their primary endpoints, in Barth syndrome, mitochondrial myopathy, heart attack and macular degeneration. The positive signals come mainly from open-label extensions and secondary measures.

Exenatide is the original GLP-1 receptor agonist, and it came out of a lizard. Exendin-4 was isolated from the venom of the Gila monster, Heloderma suspectum, and turned out to be a full agonist at the human GLP-1 receptor that resists the enzyme which destroys the human hormone. It reached the market in 2005 as twice-daily Byetta and later as weekly Bydureon, and everything that followed - liraglutide, semaglutide, tirzepatide - descends from the idea it proved. By modern standards it is weak: roughly 1% of body weight lost, and its cardiovascular outcome trial, EXSCEL, missed superiority at a hazard ratio of 0.91 with a confidence interval touching 1.00. Its most interesting current life is outside diabetes, and that story ended badly too: a promising phase 2 result in Parkinson's disease was followed by a clean negative phase 3.

GB-115 is a synthetic glycyl-tryptophan dipeptide analog of cholecystokinin studied as an anxiolytic. A Russian open-label pilot in 31 people with generalized anxiety disorder reported reduced anxiety and fatigue over 21 days, with 6 mg daily selected after a small dose-finding stage. Without a placebo group, efficacy remains uncertain.

GHK-Cu is the copper complex of GHK (glycyl-histidyl-lysine), a tripeptide found in human plasma, saliva and urine whose levels fall with age. In lab studies it raises collagen and elastin production and supports skin cells, and it is a common ingredient in anti-wrinkle products. The best human evidence is one 1994 trial in which a GHK-Cu gel sped the healing of diabetic foot ulcers. The cosmetic studies are described mainly in reviews by the peptide's discoverer, and an independent review found few published clinical studies.

GHRP-2 (pralmorelin) is a synthetic hexapeptide that releases growth hormone through the ghrelin receptor, about as strongly as hexarelin and more strongly than GHRH. Japan licensed it as a single-dose diagnostic test for growth hormone deficiency, and that is essentially its whole clinical career. It is not selective: at growth hormone-releasing doses it also raises prolactin, and raises ACTH and cortisol about as much as CRH does. Repeated dosing over days to weeks produces complex changes in the growth hormone axis, including desensitization depending on dose and frequency. There is no controlled trial of GHRP-2 for muscle, fat or strength in healthy people.

GHRP-6 is the original growth hormone-releasing peptide, the compound whose receptor turned out to be the ghrelin receptor. In people it releases about three times as much growth hormone as GHRH, and combining the two is strongly synergistic. Unusually for a growth hormone stimulus, the response barely declines with age. Its pharmacokinetics are known: after an intravenous bolus the distribution half-life is about 7.6 minutes and elimination about 2.5 hours. What does not exist is any trial of what taking it for weeks or months does to IGF-1, muscle or fat in healthy people; it also raises ACTH and cortisol, and it makes people hungry.

HDAP2 is a synthetic four-amino-acid peptide, biotin-D-Arg-Phe-Phe-D-Arg-amide, designed to bind cardiolipin, the signature lipid of the inner mitochondrial membrane, and hold it in its normal bilayer form. In mice it preserved retinal ganglion cells after optic nerve crush, and both the cells and their axons in an inherited glaucoma model, without lowering eye pressure. All of the evidence is from cells and mice, from the lab that invented and patented it. It has not been tested in people.

Hexarelin is a synthetic hexapeptide that releases growth hormone through the ghrelin receptor, and it does so more strongly than GHRH itself: 1 ug/kg intravenously produced about twice the growth hormone response of the same dose of GHRH in healthy young men. It has been studied mainly as a diagnostic agent for growth hormone deficiency, where hexarelin plus GHRH matches the insulin tolerance test. The problem with taking it is tachyphylaxis: over 16 weeks of twice-daily subcutaneous dosing the growth hormone response fell by about half, IGF-1 did not change at all, and body composition and bone density did not move. Like GHRP-2, it also raises prolactin, ACTH and cortisol.

HGH fragment 176-191 is the C-terminal tail of human growth hormone, synthesized on its own. It is the peptide behind AOD-9604, which is this same fragment with a tyrosine added, and the two share a literature. In obese mice, chronic treatment cut cumulative weight gain and fat mass, and it suppressed fat synthesis as strongly as the intact hormone, and the AOD-coded analog raised lipolytic activity in fat tissue from obese rodents and from humans in a dish. No study in this literature measured IGF-1, and no trial has ever given the peptide to a person: everything known about it comes from mice, rats and isolated cells.

Humanin is a 24-amino-acid peptide encoded not in the nucleus but inside mitochondrial DNA, within the 16S rRNA gene. It was found in 2001 by screening a surviving region of an Alzheimer's brain for factors that protect neurons from amyloid-beta toxicity, which is an unusually direct origin story. It belongs to the same class as mots-c - mitochondria-derived peptides, or mitokines, which appear to signal cellular stress from mitochondria to the rest of the body. The preclinical literature is broad: cytoprotection against apoptosis, cardiovascular effects, roles in cancer and degenerative disease and in the testis. There is no human trial. Circulating humanin declines with age, which is interesting and is not the same as a reason to inject it.

Intranasal insulin is ordinary human insulin sprayed high into the nose so that some of it travels into the brain, where insulin receptors are dense in memory regions, while blood insulin and glucose barely change. Small trials found better memory in healthy adults and in people with mild cognitive impairment or Alzheimer's, but the largest trial, a 12-month phase 2/3 study in 289 people, found no benefit. Several trials in older surgical patients reported less delirium after surgery.

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) that releases growth hormone through the ghrelin receptor. Novo Nordisk designed it in the 1990s from the GHRP-1 series, and its selling point was selectivity: in pigs it released growth hormone as strongly as GHRP-6 but, unlike GHRP-6 and GHRP-2, did not raise ACTH or cortisol even at more than 200 times the effective dose. The catch is that almost nothing has been published about what it does in people. The one controlled human trial gave it intravenously for postoperative bowel paralysis, and found no benefit over placebo. No published human study has measured growth hormone, IGF-1 or body composition on ipamorelin.

Kisspeptin-10 is the shortest natural form of kisspeptin, the hypothalamic hormone that switches on the reproductive axis. It is the ten amino acids at the end of the longer kisspeptins and keeps their full activity at the kisspeptin receptor. A single injection releases GnRH and so LH within minutes, and infusions raise testosterone in healthy men and in men with type 2 diabetes and low testosterone. It clears from the blood in about 4 minutes, so studies have used infusions, and its effects in women depend on the phase of the menstrual cycle. It is not approved for any use.

KPV (lysine-proline-valine) is the last three amino acids of α-melanocyte-stimulating hormone (α-MSH). It keeps the hormone's anti-inflammatory action without its effect on skin pigment. In mice, KPV in the drinking water eased chemically induced colitis, and it cut colitis-associated tumors. It is taken up by PepT1, a peptide transporter that is switched on in the inflamed colon. No human study of KPV has been published.

Mazdutide is a glucagon/GLP-1 dual agonist built on oxyntomodulin, a natural gut peptide that hits both receptors. It was licensed from Eli Lilly to Innovent Biologics and developed almost entirely in China, which makes its trial program unusual: every efficacy result comes from Chinese participants, who start from a lower mean body weight than the Western obesity trials. GLORY-1 gave 14.01% weight loss at 6 mg over 48 weeks against a 0.30% gain on placebo, and GLORY-2, at 9 mg over 60 weeks, gave 16.65% against a 1.50% loss. Those are tirzepatide-class numbers. The caveat is the population: whether they transfer to a heavier, more metabolically damaged Western cohort has not been tested, and a head-to-head against semaglutide is only now running.

MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA, not in the cell nucleus. In mice, injections prevented diet-induced obesity and insulin resistance and improved running capacity at every age tested. In people, exercise raises the body's own MOTS-c, but no trial has given MOTS-c to humans, and measurements of it in blood disagree between methods.

Oxytocin is a nine-amino-acid hormone made in the hypothalamus. It contracts the uterus in labor and releases milk, and in the brain it acts on social, sexual and stress behavior through a single receptor. Injected oxytocin is a standard drug for preventing bleeding after birth. As a nasal spray it raised oxytocin in the cerebrospinal fluid, but the large trials of intranasal oxytocin in autism and obesity were negative, a famous finding that it increases trust failed to replicate, and it did no better than placebo for women's sexual function.

PNC-27 is a chimeric peptide - a fragment of p53 that binds HDM-2, joined to penetratin, a sequence that carries cargo across membranes. Its proposed mechanism is unusual and specific: cancer cells display HDM-2 in their plasma membrane, normal cells do not, and PNC-27 binds that membrane-bound HDM-2 and forms pores, lysing the cell. In leukemia cells it induced necrosis while sparing normal hematopoietic cells, and later work describes additional disruption of mitochondrial membranes. It is a fifteen-year-old cell-culture program from a small group of investigators, with no human trial and no published clinical development.

Retatrutide is an experimental once-weekly injected peptide from Eli Lilly that activates three hormone receptors: GIP, GLP-1 and glucagon. In a 48-week phase 2 trial in adults with obesity, the 12 mg dose lowered body weight by 24.2%, against 2.1% on placebo. The first phase 3 trial, in type 2 diabetes, confirmed large falls in HbA1c and weight. It is not approved; in the cited literature its phase 3 obesity trials are still under way.

S-acetylglutathione (SAG) is glutathione with an acetyl group attached to its sulfur. It is sold as a supplement on the idea that it survives digestion better than plain glutathione. In the only human pharmacokinetic study, a 3.5 g dose produced no detectable SAG in the blood, and the rise in blood glutathione looked much like the rise after plain glutathione. Every other result comes from cells, animals, or one small open-label trial of a multi-ingredient product. EFSA judged it safe as a food at up to 300 mg a day for adults.

Selank is a synthetic heptapeptide (Thr-Lys-Pro-Arg-Pro-Gly-Pro) described as an analog of tuftsin. It is studied as an anxiolytic. In Russian clinical studies of generalized anxiety and related disorders, it matched the benzodiazepine medazepam on anxiety, and adding it to phenazepam reduced phenazepam's side effects. Proposed mechanisms include slowing enkephalin breakdown and modulating GABA-A receptors.

Semaglutide is the GLP-1 receptor agonist that turned obesity into a treatable condition in mainstream medicine. In STEP 1, 68 weeks of 2.4 mg weekly produced a mean 14.9% weight loss against 2.4% on placebo, with half of participants losing 15% or more. In SELECT, 17,604 people with obesity and established cardiovascular disease but no diabetes had a 20% reduction in major cardiovascular events over the trial - the result that moved it from a weight drug to a cardiovascular one. The costs are real and well documented: gastrointestinal effects in most people, about 4.5% discontinuing for them in STEP 1, and weight regain when it stops. A year after withdrawal in the STEP 1 extension, participants had regained two-thirds of what they lost.

Semax is a synthetic heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro), an analog of the ACTH(4-10) fragment of the hormone ACTH, given as a nasal spray. It is used in acute stroke therapy. In rats it raises BDNF and its receptor in the brain. Almost all of its clinical research is published in Russian, and the human studies are small and mostly unblinded.

Sermorelin is GHRH(1-29), the shortest fragment of growth hormone-releasing hormone that keeps full activity, and it is the parent of every GHRH analog including tesamorelin and CJC-1295. It was a licensed medicine: a diagnostic injection for pituitary function and, briefly, a treatment for short stature in children. It reliably releases growth hormone, but as a treatment it lost to recombinant growth hormone in head-to-head comparisons — children on daily growth hormone grew faster than children on GHRH(1-29), and in a randomized comparison only the growth hormone group gained height relative to bone age. Its half-life is about four minutes. It is no longer marketed in the US, and there is no trial of it in healthy adults for any purpose.

Survodutide activates the glucagon receptor as well as the GLP-1 receptor. Adding glucagon agonism to an incretin is counterintuitive - glucagon raises blood sugar - but it also raises energy expenditure and acts directly on the liver, and in a weight-losing context the GLP-1 arm covers the glycemic downside. The phase 2 obesity trial gave 14.9% weight loss at 4.8 mg over 46 weeks against 2.8% on placebo. The more striking result is hepatic: in a phase 2 trial in MASH, 48 weeks improved histological steatohepatitis without worsening fibrosis in 47-62% of participants against 14% on placebo, and a phase 3 trial in MASLD found 84.2% achieved a 30% or greater reduction in liver fat against 24.3%. The tolerability cost is high: vomiting in 41% against 4% on placebo in the MASH trial.

TB-500 is a product built on Ac-LKKTETQ, a synthetic, acetylated copy of the seven-amino-acid actin-binding region of thymosin beta-4. It began as a veterinary preparation and is marketed for wound healing and tissue repair. It has never been tested for efficacy in humans. In a lab study, the intact peptide did not speed wound closure; one of its breakdown products did.

Tesamorelin (Egrifta) is a synthetic version of growth hormone-releasing hormone (GHRH). It makes the pituitary release more of the body's own growth hormone. It is approved to reduce excess abdominal fat in people with HIV. In two phase 3 trials, daily injections cut visceral (deep abdominal) fat by about 15% more than placebo over 26 weeks while leaving fat under the skin alone, and it also lowered liver fat. The fat returns once treatment stops. One trial in older adults reported better executive function, but a later trial in people with HIV found no clear cognitive benefit.

Thymosin beta-4 (Tβ4) is a 43-amino-acid protein found in almost every cell, where it is the main store of unused actin, the building block of the cell skeleton. Animal studies report faster skin-wound healing, stronger repaired ligaments and improved recovery after heart or brain injury. Small human trials of topical treatment for venous ulcers and eye disease have encouraging but inconclusive findings. It is not approved as a medicine.

Tirzepatide is a once-weekly injected peptide that activates two gut-hormone receptors, GIP and GLP-1. It is approved for type 2 diabetes and, as Zepbound, for chronic weight management. In a 72-week trial in adults with obesity, the top dose lowered body weight by 20.9%, against 3.1% on placebo. In a head-to-head trial it caused more weight loss than semaglutide (20.2% vs 13.7%). Most side effects are gastrointestinal, and the weight comes back when treatment stops.